One way to multiply a number by 9 is to multiply by 10 and then subtract the number from the product.

There is another way to multiply fast by 9 and as the first one it has an analogue for multiplication by 99, 999 and all such numbers.

One way to multiply a number by 9 is to multiply by 10 and then subtract the number from the product.

There is another way to multiply fast by 9 and as the first one it has an analogue for multiplication by 99, 999 and all such numbers.

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